Generally, carbon nano materials include various nanoscale carbon structures, such as hollow tubular-like carbon nano tube (CNT), solid fiber-like carbon nano fiber (CNF), nanoscale-thickness single/multiple layered graphite sheet, globular fullerene, atomic-thickness graphene, carbon nano-horn, carbon nano-filament wall, crystallized carbon microsphere, amorphous carbon microsphere, and so on. In detail, the structures as well as configurations of carbon nano tube or the carbon nano fiber can be chained or coiled, such as carbon nano-coil tube (coiled shape CNT, coil-CNT) or coiled nano carbon fiber (coiled shape CNF, coiled nano carbon fiber). The aforementioned nanoscale carbon structures are shown in FIG. 1, which is quoted from Ahmed Shaikjee, Neil J. Coville., “The synthesis, properties and uses of carbon materials with helical morphology” Journal of Advanced Research, Cairo, 2011). In the past, the coiled shape CNT and the coiled nano carbon fiber are by-products from the CNT fabrication process. Later on, in 1989, Motojima et al. used acetylene gas as a carbon source gas to grow micro coiled carbon fibers (MCCF) by utilizing the catalyzed thermal chemical vapor deposition method.
Carbon nanocoil (coiled shape CNC) and carbon microcoil (CMC) have a unique coiled structure (see FIG. 3), a great mechanical strength, structural elasticity, and electrical characteristics, so that numerous of researchers had laid stress on them since then. More specifically, carbon nanocoil and carbon microcoil can be widely applied to various fields like electromagnetic wave absorber, sensors of magnetic field induced current, and nanoscaled mechanical components, etc.
While applying carbon nanotube to the field emission, hundred to thousand times of locally enhanced electric field can be generated at the tip of carbon nanotube due to its large depth-to-width ratio and its small diameter. As a result, carbon nanotube (CNT) or carbon nanofiber (CNF) has great electron emission properties; the work function of about 4.5 eV can be overcome, and electrons can be emitted around 1˜2 V/μm. For example, while depositing CNT or CNF on the cathode of an electric field, the electrons can be emitted from the tip or the outer surface of CNT or CNF driven by the driving force of the electric field. Then, those electrons will be collided with the phosphor layer on the anode through a vacuumed interval, thereby a light beam is emitted from the phosphor layer based on the field emission light theory. The field emission light theory is applied for developing field emission light (FEL), and field emission display (FED). For instance, in 2002, J.-M. Bonard, R. Gaal, S. Garaj et al. had published a paper (Field emission properties of carbon nanohorn films. Journal of applied physics 91 (12): 10107-10109) which illustrates that carbon nanostructure, multi/single-wall carbon nano-tube, and carbon nano-cone have great field emission properties. In addition, US Pub. No. 20030001477, U.S. Pat. No. 7,276,843, and a paper published by Pan L, Hayashida T, Nakayama Y et al. in 2002 (Fabrication of Carbon Nanocoil Field-Emitters and Their Application to Display; Japan Hardcopy Vol 2002, page 533-534) also illustrate that single-wall carbon nano-tube, cylindrical graphene, graphitic nanofibers, carbon nano-coil fiber can be used as a cathode emitter.
Coil shape CNT and coil-CNF have excellent electromagnetic-wave absorption efficiency, such an absorption efficiency of electromagnetic waves ranging from 250 to 950 MHz is about to be 90 to 95%. For instance, while mixing 1 to 2 wt % coil shape CNT into a polyurethane matrix, the electromagnetic wave absorption efficiency of the mixture even reaches −20 db, that is, an absorption efficiency over 99%. Carbon nanocoil (coil shape CNC) as well as carbon microcoil (CMC) also have good electromagnetic-wave absorption efficiency in gigahertz region (12˜110 GHz); in detail, electromagnetic-wave absorption efficiency may be enhanced by multi-layered absorbing composites with additive the coil shape CNC and/or CMC. Additionally, other outstanding properties of coil shape CNC such as its mechanical properties and hydrogen absorption properties have been taken seriously as well.
As for the aspect of fabrication processes for coil-CNT and coil-CNF, European Pat. No. 1061041 has disclosed that, by using the chemical vapor deposition (CVD) method, coil shape CNT can be grown on a glass plate, a silicon plate, and an alumina plate by utilizing cobalt, nickel, iron, chromium or palladium. In 2007, Woo Yong Sung et al. Nanotechnology 18 245603) have illustrated that coil-CNF mixed with coil shape CNT can be grown on a conductive film layer of a nickel substrate. However, the yield of CNF (or coil-CNF) by using these disclosures process is very low, not ready for practical application in industrial.
Generally, in order to reduce the energy barrier during the growth of CNT and coil shape CNC, metal catalysts are commonly used. For example, in 1998, Saito et al. published a paper titled “High yield of single-wall carbon nanotubes by arc discharge using Rh—Pt mixed catalysts” (Chemical Physics Letters 294 (1998), Pages 593-598), which utilizes rhodium or platinum as a catalyst, and US Pub. No. 20100261058 has utilized magnesium, gold, silver, ruthenium, rhodium, iridium, platinum, palladium, molybdenum, tungsten, and chrome catalysts for adhering CNT. Further, US Pub. No. 20110183105 has disclosed carbon nano materials containing coiled nano carbon material grown on oxides of cobalt, nickel, iron, and palladium. U.S. Pat. Nos. 7,074,380 and 7,923,058 have disclosed coiled nano carbon materials grown on an electrode by using thermal decomposition method with organic compound catalyst solutions containing cobalt, nickel, iron, or palladium ions. It is known from WO2004105940 that carbon nano-coil tubes may be effectively fabricated by using catalysts including carbides of transition metals, in which the transition metals is preferably iron, cobalt, or nickel, such as Fe3InC0.5, Fe3InC0.5Snw, and Fe3SnC. It is also known from WO2012038786 that, catalysts including Ni, Ru, Rh, Pd, Ir, Pt, Cr, Mo, or W; or organic acids with more than one coordination group, steroids, amino acids, peptides, phosphate, nucleotides, tetrapyrrols, ferrioxamine; ionophores such as gramicidin, monensin, valinomycin, and phenolics, 2,2′-bipyridyldimercaptopropanol, ethylenedioxydiethylene-dinitrilo-tetraacetic acid, ethylene glycol-bis(2-aminoethyl)-N,N,N′,N″-tetraacetic acid, ionophores-nitrilotrriacetic acid, salicylic acid, triethanolamine, sodium succinate, sodium acetic acid, ethylene diamine, ethylenediaminetetraacetic acid, ethylenetriaminepentaacetic acid, and ethylenedinitrilotetraatic acid, are disclosed. In WO2012038786, coil-CNF and coil shape CNC having 20 nm˜200 nm in width and 0.5 μm˜10 μm in length can be grown on a glass fiber by immersing a glass substrate with such catalysts followed by introducing into a carbon source of CH4, C2H6, C3H8, CO2, ethylene, acetylene, etc.
Furthermore, Ding et al. have published a paper in 2003, “Ni—Ni3P Alloy Catalyst for Carbon Nanostructures, Chemical Physics Letters, Vol. 371, pp. 333-336” illustrating that by adding a few phosphorous and sulfur, decomposition of hydrocarbon molecules can be facilitated, and thus enhancing the yield of coil-CNT. However, in practice, the fractional yield and purity of coil-CNF and coil-CNT fabricated by using those aforementioned processes and techniques are low that is insufficient for practical application, such as using in electric field emission or the microwave absorption.